The density of the integrate circuits has been increasing over the past years to meet the higher performance required of the integrated circuits. Package size is getting smaller and smaller to meet the same high performance requirement resulting in higher pin density for the package. Higher pin density requires finer pitch of I/O connecting leads. Ball Grid Array packages meet the higher density pin requirements and are being used to replace current Quad Flat Package (QFP) due to the advantages of the BGA over the traditional QFP package.
BGA packages have less coplanarity problems, have self-alignment capability, and have better yield than QFP packages.
There are many kinds of ball attach technologies available, but they are all complicated in the ball attach process, and hard to get uniform balls on the substrate.
One example of ball attach is the use of a dispensing machine to dispense solder paste on the substrate directly. Since the deposited solder paste may vary in volume, each solder ball may have a different metal content. It is hard to control the solder ball height. The productivity of dispensing method is lower, but the major issue is the short ball height.
Another process is the attachment of preformed balls. There are two methods, one for plastic packages, and one for ceramic packages. A Eutectic solder ball is used for plastic BGA packages and a high temp solder ball is used for ceramic BGA packages.
A solder wire bond is used to form BGA balls. A wire bonder is to bond solder wire on the lead pads of substrate. The solder wire is then reflowed to melt solder into balls. This process has low productivity and low solder ball height problems.
A punch metal pellet Ball attachment process is a common method used to form the balls on a BGA package Visual inspection system must be used to ensure 100% ball placement.
Each of the above processes does not ensure uniform ball height or size, nor ensure that a ball is placed at each desired place on the semiconductor package.